Testogel is a transdermal testosterone replacement therapy licensed in the UK for treating male hypogonadism, a condition where the testes produce insufficient testosterone. Applied daily as a gel to the shoulders and upper arms, it delivers testosterone through the skin into the bloodstream, restoring physiological hormone levels in men with confirmed deficiency. Treatment should only be initiated following biochemical confirmation of low testosterone alongside relevant clinical symptoms such as reduced libido, fatigue, or decreased muscle mass. This article explains what Testogel does, its expected benefits, potential side effects, and important safety considerations for patients considering or currently using this treatment.

What Is Testogel and How Does It Work?

Testogel is a transdermal testosterone replacement therapy (TRT) licensed in the UK for treating male hypogonadism—a condition where the testes produce insufficient testosterone. It is available as a clear, colourless gel containing testosterone, most commonly as Testogel 16.2 mg/g (supplied in a metered-dose pump or sachets). Patients apply the gel once daily to clean, dry, intact skin on the shoulders and upper arms only (not the abdomen or genitals), as specified in the UK Summary of Product Characteristics (SmPC).

The gel works through percutaneous absorption, allowing testosterone to pass through the skin into the bloodstream. Once absorbed, testosterone circulates systemically and binds to androgen receptors in various tissues, including muscle, bone, and the central nervous system. This mimics the body's natural testosterone production, helping to restore physiological levels in men with confirmed deficiency.

Mechanism of action involves testosterone's conversion to dihydrotestosterone (DHT) in some tissues and to oestradiol in others via aromatisation. These metabolites contribute to the hormone's diverse effects on sexual function, muscle mass, bone density, and mood. The transdermal route provides steady-state testosterone levels within a few days of starting treatment, avoiding the peaks and troughs associated with intramuscular injections.

Testogel should only be prescribed following biochemical confirmation of hypogonadism—typically two separate early-morning serum testosterone measurements below the normal reference range for the local laboratory—alongside relevant clinical symptoms such as reduced libido, erectile dysfunction, fatigue, reduced muscle mass, or mood disturbance. Additional investigations should include luteinising hormone (LH), follicle-stimulating hormone (FSH), sex hormone-binding globulin (SHBG), and, where secondary hypogonadism is suspected, prolactin and pituitary imaging. NICE guidance emphasises that testosterone replacement is not indicated for age-related decline in testosterone alone without clear biochemical deficiency and symptoms. Treatment is usually initiated by an endocrinologist or specialist with experience in male hypogonadism, often with subsequent shared care involving the GP according to local protocols.

Expected Benefits and Timeline of Testogel Treatment

Men with confirmed testosterone deficiency may experience a range of benefits from Testogel, though the timeline varies depending on the specific effect. Understanding realistic expectations helps patients remain adherent to treatment and recognise when therapy is working.

Sexual function improvements often appear relatively early. Increased libido may be noticed within 3–6 weeks, whilst improvements in erectile function typically develop over 3–6 months. However, testosterone replacement alone may not fully resolve erectile dysfunction if other factors (vascular disease, diabetes, psychological issues) are present, and additional therapies such as phosphodiesterase-5 (PDE5) inhibitors may be required.

Mood and quality of life changes generally emerge within 3–6 weeks, with patients reporting improved energy levels, reduced fatigue, and better overall well-being. Depressive symptoms associated with hypogonadism may also improve, though testosterone is not a treatment for clinical depression and should not replace appropriate psychiatric care.

Physical changes require longer timeframes:

• Body composition: Decreased fat mass and increased lean muscle mass become apparent after 12–16 weeks, with maximum effects at 6–12 months

• Bone density: Improvements continue for at least 2–3 years of treatment

• Haemoglobin levels: Increases typically occur within 3 months, plateauing at 9–12 months

Monitoring response is crucial. Serum testosterone levels should be checked after starting or adjusting treatment, with blood samples taken at the time specified in the SmPC for the formulation used (commonly 2–4 hours after gel application for Testogel 16.2 mg/g). Target levels should be within the mid-normal adult male range for the local laboratory and time of sampling. Dose adjustments may be necessary based on clinical response and biochemistry, following the SmPC guidance.

It is important to note that not all symptoms reverse completely, particularly if hypogonadism has been longstanding or if other medical conditions contribute to symptoms. Patients should maintain realistic expectations and continue regular follow-up with their healthcare provider.

Potential Side Effects and What to Monitor

Like all medicines, Testogel can cause side effects, though not everyone experiences them. Understanding what to monitor helps ensure safe, effective treatment.

Common local reactions include:

• Skin irritation, dryness, or redness at application sites (affecting up to 1 in 10 users)

• Acne or oily skin, particularly on the face, chest, and back

• Increased body or facial hair growth

These effects are generally mild and may improve with continued use or by rotating application sites within the permitted areas.

Systemic side effects can include:

• Polycythaemia (increased red blood cell production): This is one of the most important adverse effects to monitor. Elevated haemoglobin and haematocrit increase blood viscosity and potentially raise cardiovascular risk. Full blood count should be checked at baseline, 3 months, 6 months, 12 months, and then annually. If haematocrit exceeds 0.54 (or haemoglobin >170 g/L), treatment should be interrupted or the dose reduced, and secondary causes of erythrocytosis investigated

• Prostate effects: Testosterone can stimulate benign prostatic hyperplasia (BPH) or, theoretically, prostate cancer growth. Prostate-specific antigen (PSA) testing and digital rectal examination (where appropriate) are recommended at baseline, 3–6 months, 12 months, and then annually, particularly in men over 50

• Mood and behavioural changes: Some men report increased irritability, mood swings, or aggression. These are recognised adverse effects in the SmPC and should be reported to your doctor

• Fluid retention: Mild ankle swelling may occur, particularly in men with cardiac, hepatic, or renal impairment

• Gynaecomastia: Breast tissue enlargement can develop due to testosterone's conversion to oestradiol

When to seek medical advice:

• Persistent skin reactions that do not improve

• Signs of polycythaemia (headaches, dizziness, visual disturbances, flushing)

• Urinary symptoms (difficulty passing urine, increased frequency, poor stream)

• Chest pain, leg swelling, or breathlessness

• Significant mood changes, depression, or increased aggression

Transfer risk: A critical safety consideration is inadvertent testosterone transfer to others through skin contact. Women and children are particularly vulnerable to virilisation and premature sexual development. Application sites must be covered with clothing once the gel has dried, and hands washed thoroughly with soap and water immediately after application. Partners and children should avoid contact with application areas. If skin-to-skin contact occurs, the exposed person should wash the area with soap and water as soon as possible. Patients should wait at least 6 hours (or as specified in the SmPC) before showering or swimming. The gel is flammable until dry; avoid fire, flames, or smoking until the application site is completely dry.

Reporting side effects: Suspected adverse reactions should be reported via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Who Should Not Use Testogel and Important Precautions

Testogel is contraindicated in several situations where testosterone replacement could cause harm or is inappropriate.

Absolute contraindications include:

• Prostate cancer or breast cancer (current or previous)

• Hypersensitivity to testosterone or any gel excipients

• Women and children: Testogel is not licensed for female use and poses virilisation risks. Accidental exposure in children can cause premature sexual development

Relative contraindications and cautions require specialist assessment:

• Cardiovascular disease: Men with heart failure, recent myocardial infarction, or stroke require careful evaluation. The MHRA has issued guidance advising caution in men with cardiovascular risk factors, and individual cardiovascular risk assessment should be undertaken before and during treatment

• Severe sleep apnoea: Testosterone may worsen this condition

• Polycythaemia: Pre-existing elevated haematocrit (>0.54) or haemoglobin (>170 g/L) should be investigated and managed before starting treatment

• Severe lower urinary tract symptoms: Significant BPH may worsen with testosterone

• Severe cardiac, hepatic, or renal insufficiency: Risk of oedema and fluid retention

• Epilepsy or migraine: These conditions may be exacerbated

Important precautions during treatment:

• Regular monitoring is essential: testosterone levels (at the SmPC-specified time after application), full blood count (baseline, 3, 6, 12 months, then annually), PSA and digital rectal examination as appropriate (baseline, 3–6 months, 12 months, then annually), liver function tests, and lipid profile should be checked according to specialist protocols

• Fertility considerations: Testosterone replacement suppresses spermatogenesis and can cause infertility. TRT is not appropriate for men actively trying to conceive. Men wishing to father children should be referred to andrology or reproductive medicine services for fertility-focused treatment options

• Drug interactions: Testogel may affect anticoagulant requirements, diabetes medications, and corticosteroids. Inform your doctor of all medicines you are taking

• Application technique: Patients must apply gel to clean, dry, intact skin on the shoulders and upper arms only (never to the abdomen or genitals), allow complete drying, cover the area with clothing, and wash hands thoroughly with soap and water after application

• Red-flag symptoms: Contact your GP or specialist urgently if you develop severe headaches, visual disturbances, or neurological symptoms, as these may indicate pituitary pathology requiring investigation

Patients should contact their GP or specialist if they develop new symptoms, particularly urinary changes, chest pain, leg swelling, breathing difficulties, or significant mood changes. Ongoing monitoring under shared-care protocols (where the specialist initiates treatment and the GP provides follow-up according to local agreement) is typical in the UK. Testosterone replacement is usually a long-term commitment requiring sustained adherence and regular follow-up to ensure safety and effectiveness.

Frequently Asked Questions